A wealth of experimental evidence points to the importance of decreased mitochondrial function and increased oxidative stress in age-related neurodegenerative conditions such as Parkinson's Disease (PD). Dopamine- producing nerve cells in the midbrain region of PD patients exhibit both of these defects, and eventually die due to progressive accumulation of cellular damage. The studies outlined in this proposal are designed to assess the role of FoxO family transcription factors in protecting dopaminergic neurons from oxidative stress and mitochondrial dysfunction. FoxO factors are directly implicated in cellular longevity and stress resistance, suggesting that long-term maintenance of quiescent neurons is dependent upon continued FoxO activity during the aging process. To determine whether FoxO activity is required for survival of dopaminergic neurons, the mammalian FoxO genes (FoxO1, FoxO3 and FoxO4) will be simultaneously deleted from these cells in mice using conditional knockout technology. The effects of FoxO deletion will be tested in live mice using defined physiological assays to measure motor performance and striatal dopamine content (Aim 1), and in cultured primary neurons using a battery of assays to measure oxidative stress and mitochondrial function (Aim 2). Loss of FoxO factor expression is expected to cause progressive neuronal cell death in mice due to the accumulation of cellular damage from unrestrained oxidative stress and decreased mitochondrial energy production.